Mining_Methods_UnderGround_Mining - Mining and Blasting

keMi, Finland
Kemi underground mine – simplified long section.
produced from open pits, resulting in
130 million t in the waste heaps.
Ore grade control
Ore grade control in both the open pit
and the underground mine involves intensive
wire line diamond core drilling,
to determine boundaries and qualities
of specific ore types. In addition, all
blast holes in the open pit are sampled.
Technical innovations for ore characterization
and quantification include
OMS-logg down hole logging, and automated
image analysis for establishing
grain size distribution.
Basic production data about mineralogical
and process histories are logged
Atlas Copco Diamec U6 APC at work underground.
for each ore stope on a daily basis, and
this is merged and compared with daily
and blast-specific production histories
from the database.
Each ore blast is treated selectively at
the concentrator, in order to minimize
feed variation and maximize process
stability.
In the concentrator, total chromite
recovery is around 80%, depending on the
proportion of lumpy ore. Metallurgical
grade concentrate contains about 45%
Cr 2O 3 of 0.2 mm grain size, while upgraded
lumpy ore is about 35% Cr 2O 3
with 12-100 mm size. The former is pelletised
at Tornio, and then mixed with
upgraded lumpy ore before smelting to
produce ferrochrome.
Concentrator operation is optimized
by accurate calibration of the feed slurry
analyzers, and control of product quality
from each unit process, both by com-
pensating for changes in feed type, and
measuring product quality on-line.
Manual input can be used, as well as
on-line information.
A Craelius Diamec 264 APC drill rig
carries out 10 km of coring each year.
Drill sections are established every 10
m and downhole survey is standard procedure,
using a Maxibore system. Based
on the drill hole data, a 3D model of the
orebody is created and used as a basis
for production planning. Tying all these
streams of collected data and planning
outputs together requires an extremely
fast communications network, interfacing
with a single master database.
underground infrastructure
The main decline starts at a portal in
the footwall side of the pit, at about 100
m below the rim. The decline is mostly
8 m-wide x 5.5 m-high, to accommodate
passing vehicles. It descends at 1:7
to a depth of 600 m at the base of the
hoisting shaft, and connects with several
intermediate sublevels. The decline
is asphalted throughout most of its
length.
There is also a 5,000 cu m repair
shop for open pit equipment at the 115 m
level, and a larger 14,000 cu m workshop
at the 350 m level for the underground
mobile equipment fleet. The
final 23,000 cu m main workshop is at
the 500 m level. The 350 m level workshops
are enclosed by megadoors, which
keep in the heat so that an ambient 18
degrees C can be maintained. The service
bay is equipped with a 10 t travelling
gantry and 16 m-long inspection
pit. The washing bay is equipped with
two Wallman hydraulically controlled
washing cages, so there is no need for
operatives to climb onto the mobile
equipment.
The main pumping station is located
at the 350 m level, and has pumping
capacity of 2 x 250 cu m/h. The slurrytype
pumps, with mechanical seals,
pump the unsettled mine water to the
surface with a total head of 360 m. Two
other dewatering pumping stations are
located at the 500 m and 580 m levels.
64 underground mining methods